If you're someone who doesn't need glasses or contacts, you probably think you don't need to get your eyes checked this year (or ever?). But regular eye exams can check for more than just your ability to read the letter W from very far away.

When it comes to how often you should get an eye exam, the recommendations vary depending on the organization, your age, and whether or not you have any known vision issues or health conditions that affect your vision. (Plus, of course, what your insurance will cover.)

Jeffrey Whitman, M.D., an ophthalmologist based in Dallas, tells SELF that he recommends adults over 40 see an ophthalmologist once a year for a complete fully-dilated exam. For adults 40 and under, he suggests an exam every two years. Basically, it depends.

And while routine eye exams are great, that's not the only reason to see your eye doctor.

“People typically see their eye doctors hoping to improve their eyesight, but what they often don’t realize is that over 200 major, systemic diseases have eye involvement as part of the disease course,” Alan Mendelsohn, M.D., an ophthalmologist based in Hollywood, Florida, tells SELF. “Ophthalmologists are positioned perfectly to be able to identify these illnesses before anyone else and get patients to appropriate treatment before symptoms develop or progress."

"It’s not just about glasses or contacts," says Whitman. "We need to pick up on things before they are a problem.” And those problems don't necessarily need to be related to your vision—it turns out that your eyes can offer a window into many other bodily systems, alerting eye doctors to potential issues way beyond your contact prescription. Here are few eye symptoms worth getting checked out:

1. You have a white, gray, or blue ring on the cornea (the top layer of the eye).

This is called corneal arcus or arcus senilis, and it may also appear as a white ring in front of the periphery of the iris (the colored part of the eye). In older adults, it’s a generally harmless sign of aging and not associated with any particular disease. But, according to the American Academy of Ophthalmology, it can be a sign of high cholesterol in people under age 40. Your eye doctor can confirm the condition—and the next test should be of your cholesterol levels.

2. Your eyes seem to be protruding more than usual.

Bulging or protruding eyes (proptosis or exophthalmos) can be a sign of Graves' disease, a disorder causing overactivity of the thyroid gland (hyperthyroidism). Both George and Barbara Bush had the condition, Dr. Whitman says. “The muscles thicken and push the eye forward," he says, "making it difficult for the eyelids to cover, and they become dry and uncomfortable.” These eye symptoms are referred to Graves' ophthalmopathy.

Graves' disease is often treated by an endocrinologist or radiation oncologist, sometimes with radioactive iodine therapy, though that can actually increase your risk or worsen symptoms of Graves' ophthalmopathy. Treating Graves' ophthalmopathy can include over-the-counter artificial tears, corticosteroids, or surgery, in severe cases; though symptoms often decrease on their own eventually.

3. Your eyes are always red.

Occasional redness of the eyes may be a sign of allergies, eye fatigue, over-use of contact lenses, or an infection such as pink eye (conjunctivitis). However, persistent redness—particularly when combined with other symptoms like double vision or pain with eye movement—may be a sign of an autoimmune condition, such as rheumatoid arthritis, lupus, or multiple sclerosis (MS).

“Often, one of the first organs affected is the eye,” says Dr. Mendelsohn. “In MS, in particular, up to 20 percent of patients initially complain of a seemingly unusual set of symptoms: sudden vision loss in only one eye, pain with eye movement, or double vision.”

If an autoimmune disease is the culprit, eye doctors can often diagnose the root cause of patients’ symptoms during a thorough exam and refer them to the appropriate specialist for immediate treatment.

4. You have a lot of floaters.

Eye floaters are small spots or strands that float around in your field of vision. According to the National Eye Institute, they are part of the natural aging process and usually harmless. However, having a lot of floaters may be a sign of diabetes, Lama Al-Aswad, M.D., associate professor of Ophthalmology at Columba University Medical Center, tells SELF.

Diabetes can cause blockages in the eye's blood vessels, making them bleed or leak fluid, Dr. Al-Aswad explains. Eventually, this causes diabetic retinopathy. “In the early stages of the disease the patient might have no symptoms, but later they may experience fluctuation of vision, impaired central vision and color vision, a lot of floaters and vision loss," she says. "If untreated, it can cause total vision loss.” Laser treatment is usually very effective at preventing vision loss, if done before the retina has been severely damaged.

5. You have droopy eyelids.

Very droopy eyelids may be a sign of myasthenia gravis, a neuromuscular disorder that causes weakness in skeletal muscles (the muscles the body uses for movement). Other symptoms include muscle fatigue and problems chewing and swallowing. If your doctor suspects this is causing your eyelid droopiness, you'll be sent for further tests to confirm the diagnosis, then prescribed oral medications to control it, Ming Wang, M.D., Ph.D., a Tennessee-based ophthalmologist, tells SELF.

Bottom line: If something is up with your eyes, don't brush it off. Check in with an eye doctor—even if you've always been blessed with pretty perfect vision. It can't hurt to see what's up.

Correction: This post has been updated to clarify that radioactive iodine therapy is a possible treatment for Graves' disease, but it may worsen symptoms of Graves' ophthalmopathy. An earlier version of this post mistakenly reported that radioactive iodine therapy was a treatment for Graves' ophthalmopathy. H/T Graves' Disease and Thyroid Foundation for pointing out the error.